Twitter imposes a 140-character limit on messages, requiring that authors make every word count.
To “consider” or to “contemplate” are long words, and character-hogs. The Middle English word “mull” gets the same work done.
The Oxford English Dictionary lists the verb “mull” as of unknown origin. It could be from the noun, “mull,” which in turn comes from the Old English “myl,” meaning dust or mould.
Thus, people may have started with a noun for dust and made it a verb for pulverizing something into dust. That physical action was then the basis for a verb having to do with analyzing or breaking conceptions up into their constituent parts in one’s mind. It then came to have the connotation of to consider or contemplate.
In the sense of “to grind to powder” it occurs in 1440 A.D.: “Promptorium Parvulorum (Harl. 221) 348 Mullyn, or breke to powder, or mulle, pulveriso.”
(This source is an English-Latin Dictionary, the “Storehouse for Children,” of 1440).